98. If two sequences are 1 PAM apart, then they will be:
(a) 1% identical amino acid residues,
(b) 1% similar nucleotide bases,
(c) 99% identical amino acid residues,
(d) 99% similar nucleotide bases

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Detailed Explanation:

In bioinformatics and molecular evolution, PAM (Point Accepted Mutation) units are used to measure the evolutionary distance between protein sequences. The concept was introduced by Margaret Dayhoff to model how protein sequences evolve over time.

What is 1 PAM?

• 1 PAM refers to the amount of evolutionary change that results in 1 accepted point mutation per 100 amino acids, meaning 1% of the amino acids have changed due to mutations that were not deleterious and thus were accepted by natural selection.

• Importantly, this does not mean that the two sequences are only 1% identical. In fact, they are still approximately 99% identical because only 1% of positions have changed.

Application of PAM:

PAM matrices (like PAM1, PAM250) are substitution matrices used for sequence alignment. A PAM1 matrix is built using sequences that are 1 PAM unit apart — about 99% identical. As the number of PAMs increases, the evolutionary distance increases, and the similarity between sequences decreases.

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Conclusion:

If two sequences are 1 PAM apart, they are 99% identical in their amino acid residues, making option (c) the correct answer.